The problem with simply plugging tunnels

As the MTA and transit community at large begin to examine how best to move forward with protecting the system, somehow plugging the tunnels will take center stage during the debate. The MTA saw first-hand during Hurricane Sandy that a storm surge of 13 feet will swamp eight subway tunnels and two road tunnels between Manhattan and the land mass known as Long Island. Protecting that infrastructure from future flooding is of utmost importance, but even doing so raises some delicate issues.

During my Problem Solvers discussion on Wednesday night, MTA Bridges & Tunnels President James Ferrara spoke about protecting the infrastructure but as part of a larger conversation the city needs to have. During our panel discussion, Ferrara seemed a bit more skeptical than I am that another storm will arrive. He understands that it’s very costly to harden transportation infrastructure and seemed to believe that we shouldn’t do so for storms that happen once every 100 years. Of course, we’ve now had two hurricanes in two years along with a variety of other weird weather patterns, and the oceans are getting warmer.

But protecting the Montague St. Tunnel or the Brooklyn-Battery Tunnel from future flooding isn’t as easy as installing a plug or dropping doors across the tunnel entrances. As Tom Abudllah, Transit’s Chief Environmental Engineer, said during my talk, the water has to go somewhere. If you seal off the tunnels, the water goes into the stations, and if you seal off the stations, well, then the water winds up all over the place at street level.

This realization played itself out in the media earlier this week when Joe Lhota started talking about shoring up the Brooklyn-Battery Tunnel. “I had one very prominent real estate builder who owns buildings in lower Manhattan—actually all over the city—thank me for allowing the Brooklyn-Battery tunnel to be used as a drainage ditch. I wasn’t particularly pleased with the comment,” he said to Capital New York’s Dana Rubinstein. “The fact of the matter is, if I plug it up, we plug it up, the MTA plugs it up—if God forbid this happens again, the surge is the same or even higher, the water will go elsewhere.”

In Lower Manhattan, “elsewhere” means into buildings that house multi-national corporations and into expensive housing that’s popped up downtown over the past ten years. Bill Rudin was the real estate scion who thanked Lhota, and the two engaged in a weird sort of back-and-forth over Lhota’s comments. That’s pretty much besides the point.

Ferrara spoke to this issue on Wednesday night at the Transit Museum, and he noted that we can’t just talk about protecting tunnels in a vacuum. It has to be part of a larger community discussion about protecting areas, neighborhoods, regions from the impact of flooding, storm surges and rising tides. This discussion has the potential to devolve into inaction though. Residents will come to appreciate having the Brooklyn-Battery Tunnel and other infrastructure as “drains” while those in charge of the infrastructure need to find a way to protect it. Someone will have to step into moderate, and our elected officials haven’t shown much leadership on, well, anything. It’s probably naive to expect them to find the ability to solve this more complex problem.

Ultimately, we have to remember that fixing these vulnerabilities isn’t as simple as unilateral MTA action. It’s never that simple, and the water doesn’t just disappear. So sooner rather than later, we’ll see this prickly process begin. Will real estate interests dominate transit? If history is any guide, it’s going to be an uphill battle to protect those tunnels.

Sea water inside a subway tunnel has both short term, and long term consequences that are far more costly than sea water filled stations. But in most cases, it won’t be an either/or option. If subway tunnels are allowed to flood, they eventually flood the station too.

Subway stations usually have multiple entrances and vents. It is hard to make them impregnable to water. A subway tunnel has just one way in: most of the water-logged tunnel flooded from only one direction. Stop THAT, and you’ve protected the whole tunnel.

All subway stations have many entrances and vents, and plugging all of them will be nearly impossible, unless you have either the money or time. Besides, there are third rails and signal cables in the tunnels that can be damaged as well.

Whitehall’s open for the R train again; upper South Ferry is turning 1 trains, even if the platform would need a lot of rehab work. But lower South Ferry is in need of $600 million in repairs, in large part because the first two stations had outlets for the flood waters to drain away from them and the new station didn’t (even if, in upper SF’s case, its ‘drain’ was in part the lower SF station downgrade where the upper loop tunnels met the connection to the lower station south of Rector — the not-quite-four-year-old station basically died to save the 104-year-old station’s life).

That’s why plugging the tunnels is counterproductive. You’re just kicking the can — or the water bottle in this case — to a higher elevation location, causing the problems there instead of further downhill. Making the tunnels and their components as waterproof and/or as removable as possible, and making sure any vents in flood-prone Zone A areas are moved above the high-water levels from Sandy is the best way to go (and in the case of a station like SF-Whitehall that you know will flood, those are the entrances where door plugs would make the most sense, to try and keep as much floodwater at street level as possible).

I had one very prominent real estate builder who owns buildings in lower Manhattan—actually all over the city—thank me for allowing the Brooklyn-Battery tunnel to be used as a drainage ditch.

That’s ridiculous. The tunnels just aren’t that big compared to the Upper Bay, so letting them fill didn’t reduce the water level in the city by a meaningful amount. And even if the tradeoff was public tunnels vs. rich dude’s basements, the former should win because they enable commerce for hundreds of thousands of people across the city, rather than just reducing the profits for one person who should have paid for enough insurance to cover potential damages.

It depends on the length of peak surge. If it takes an hour to fill, and the peak surge period is an hour, then the tunnels did alleviate some flooding in Lower Manhattan in the locations adjacent to the tunnel entrances.

Here again we’re faced with the problem of who takes the brunt of the storm surge, vs. who gets protected and at what cost, when I contend that it should NOT be “us or them”. The cost of protecting every element of the city’s infrastructure individually should be weighed against the cost of protecting most of the lower Hudson estuary as a whole.

Remember: This was just a tropical storm on steroids, barely qualifying as a Category 1. What happens when a churning Category 3 – or worse – comes barreling up the estuary? Will it matter which homes got flooded if Indian Point nuclear plant has a meltdown and makes the entire region uninhabitable? And the same goes for Salem and Three Mile Island.

If we’ve learned any lesson since the start of the millennium, it is that we’re all just but one big storm from having our own Fukushima-Daiichi catastrophe. And we’re not completely immune from tsunami, either – which would only give us hours to prepare instead of days.

I agree. Cutting off the water from even entering the harbor in the first place will certainly minimize the amount waterfront retrofits the MTA, PATH, City and private owners have to make. The wall would have to be pretty tall to hold back all that water that would have entered the harbor though

Its not that simple. Lets say that we had a barrier where the Lower NY Bay met the NY Bight. We would need to raise the Rockaways and Sandy Hook like Galveston did after their catastrophic hurricane in 1900.

We also need to stop giving so much weight on the top wind speed. It is important, but so are the speed and trajectory of the storm. The size of the storm and size of the high velocity wind field are also very important when it comes to storm surge height. The land fall can timing can exacerbate or minimize the impact too due to the tides.

It’s sure not that simple. First of all, blocking off the estuaries just makes you more vulnerable to rainfall behind the seawalls causing river-side flooding (the rivers are the drains, you know).

Second, the expected flooding levels call for very substantial construction… or evacuation. The 20-foot sea level rise is much more likely than the NYT thinks, given that it will happen if Greenland melts, which is happening faster than scientists expected.

Seawalls could potentially be breached during a severe enough storm. If rising sea levels are a problem, well, you’ve just made low lying NY real estate near the water uninsurable. As it is, insurance companies are refusing to issue new policies for coastal New York.

Building a sea wall would take decades to complete, and years just to do the engineering studies. Meanwhile, we will have had how many hurricanes by then?

Compared to having no wall, the breaching of sea walls would admit only a tiny fraction of the water behind it – unless you’re expecting a tsunami half the height of the Palisades – in which case all arguments for or against become completely meaningless.

Yes … building sea walls might take decades to complete. Of course, that depends entirely on how big the commitment is to get them built.

We don’t know how many hurricanes will come up our way by then. Maybe none. Maybe 30. But I’d prefer to think that even 10 or 20 years from now, there will still be a city here worth protecting.

Are you suggesting, Justin, that the fact that it might take a long time is a justification for not doing it? Because I’ve never heard of any major infrastructure project where that logic applied.

Actually – no. The lower Hudson never floods from rain. The Hudson is a tidal estuary for more than a hundred miles. It’s rise due to heavy rains is barely perceptible.

And since during an approaching storm, the sea gate would always be closed at low tide, it leaves more than enough room for rainfall. Besides, the sea gates would never be closed for more than a day – and in most cases, half-a-day.

The insurance industry is not buying this talk of walls that will take decades to build, and that’s if they even work. More people and businesses will have to relocate from low lying areas. Some strategic assets like the WTC might be protected, but unfortunately most residential areas won’t be.

Not “just a tropical storm on steroids”: if Sandy had been as small as the typical hurricane, it would have made landfall at Atlantic City as a force 3 hurricane. That’s before you take into account all the energy it got from the non-tropical part of the storm system.

The tsunami risk for New York Harbor is low: you’d have to drop half of one of the Azores into the Atlantic as a single landslide to have a serious effect here, given the plate tectonics. Yes, it could happen, but that’s a hundred-thousand-year risk.

One thing that worries me about the proposed fixes is someone at the MTA was talking about raising the subway entrances and ventilation grates. They clearly haven’t thought about this from the viewpoint of the people who are trying to walk along the sidewalks: some people now walk around rather than over the grates, but actually raising them would narrow a lot of sidewalks, many of them on already-overcrowded streets. Walking is transportation, and almost everyone who takes the subway walks at both ends.

They’d also make the subways that bit more difficult for those of us with bad knees. On a good day, I can and will climb the stairs if there’s no escalator or elevator, but I keep track of total flights of stairs, and this would add about four to a simple round trip. On a bad day, I only use accessible stations: how does he propose to keep those stations ADA-accessible if they raise the entrances 4-6 feet? Those elevator entrances are at street level.

They are not going to raise the entrances 4-6 feet. What they will do at most is to raise them a foot so that you have to climb 3 stairs before going down the way Bowling Green already is. That protects from torrential rains and small floods. It is just not practical to raise everything to level high enough to avoid what happened during Sandy. As for the street grates, I expect them to do what they have done on Steinway in Astoria — the grates are about foot high and serve as benches, but once again these measures protect against torrential rains when the streets become rivers. They will not save us from Sandy 2.

The only way to raise the the entrances high enough is if NYC decides to fill in the streets in Lower Manhattan. And fill them high — about 9 feet above where they are now. All of them. This would require all buildings currently there to be retrofitted so that what is their current second floors become their ground level floors after the filling (and the current ground floors become first basements). That is probably much cheaper than building billion dollar barriers in the sea, but I do not expect it to happen because it is a pretty radical solution.

Many buildings were raised, but some were not (especially depending on neighborhood), and you can see this in some parts of the city where homes have a bridge from the sidewalk to what was clearly built as the second floor. See: http://goo.gl/maps/lEf3C

“Not “just a tropical storm on steroids”: if Sandy had been as small as the typical hurricane, it would have made landfall at Atlantic City as a force 3 hurricane.”

What is this based on? I’m not sure I follow it.

“The tsunami risk for New York Harbor is low: you’d have to drop half of one of the Azores into the Atlantic as a single landslide to have a serious effect here, given the plate tectonics. Yes, it could happen, but that’s a hundred-thousand-year risk.”

Agreed. It is the only one known. But we also know that Earth, like any other planet, is subject to being hit by asteroids/comets. And since most of our planet is ocean, the odds are greater that a space stone would strike water than land. So there is also that – albeit rare – threat of tsunami.

Regarding the elevation of vent grates and entrances, I suspect that these are only being proposed within what is our new definition of “Zone A”. Less than 5% of the stations.

Plugging The Tunnels CANT Flood The Streets…
I think everyone will agree, there’s been no other group of water hydraulics experts smarter than the ancient Romans. Their water supply facilities still operate after 2,000 years. According to all of their engineering paradigms, plugging the tunnels CANNOT add any additional flooding to the streets. Why? In the words of Pliny: “Water Will Invariably Rise To The Height Of Its Source”.

In other words, the waters in the flooded area will always rise to the same level as the waters supplying the flood. In this instance, plugging the tunnels wont add or subtract anything at all to an existing flood situation above them. The tunnels are simply not a part of this particular hydraulics equation.

In addition to the potential raising of the street level above the flood plain as has been done in places like Seattle’s Pioneer Square area, one could follow Sinagpore’s route and build underground caverns to take in flood waters that would then be released more slowly. Some of that is already underway in NYC as part of dealing with combined sewer runoff after storms so that untreated sewage doesn’t pollute the harbor, but something similar could be done to address floodwaters (essentially diverting flooding from key infrastructure into the flood control works).

The costs would be quite steep, and I think it would probably be cheaper and more cost effective to consider a flood control barrier across the Narrows, across Raritan Bay between SI and NJ, and LI Sound from Orient Point to CT rather than try stopgap efforts that would minimize but not prevent flooding.

And the benefit of building those as flood control projects could be a piggybacking of bridging to allow rail/vehicle traffic another route between LI and the mainland as well as SI and Brooklyn.

Actually Seattle has done something similar (on a smaller scale) as part of dealing with stormwater (CSOs, combined sewer outflows). We dug a tunnel under Queen Anne Hill which is used to hold excessive amounts of stormwater for later treatment. Maybe when you all finish Water Tunnel #3 you can start digging a big cavern for stormwater.

Or maybe it would be cheaper to build the flood barrier. But you need to do something.

We have already started building storm water containment vessels. There are several in the boroughs. They’re big tanks – the size of several football fields – and they’re just designed to take storm drain overflow and hold it until after the rains pass and the water can be processed.

One problem I see is that the people of the NYC area are, as usual, acting like all human history is limited to the NYC area and started when the Europeans came.

There are other places in the world that have been dealing with flooding, storms, etc., for centuries, even millennia. I’m mostly familiar with the Netherlands and northern Germany, but I’m sure there are others.

Many of the “solutions” people are proposing — especially sea walls — have been tried, and they have problems. For instance, sea walls end up just making the waves (such as storm surges) higher.

Another problem is that no one dares state the obvious: that some real estate, including some very expensive real estate, shouldn’t be built on at all (e.g., the Rockaways, or landfill on the Manhattan shore line.)

From what I heard, historically as the city sank they just added floors. Perhaps high rises aren’t such a bad idea on the waterfront after all. As long as the building equipment is located on an upper floor, and people are prepared to travel by gondola.

Perhaps … but if we’re prepared to bore anything 45 feet in diameter and 6 miles long, there damn well better be a trains running through it.

And maybe that’s the solution to getting funding for more rail infrastructure! We just have to pitch it as sacrificial tunnels to take on storm surges. We’ll tell the public and the political powers that be that the tunnels are needed to mitigate the effects of impending rising tides – we’ll bore the tunnels to save the city from future storm surges.

Of course, once the tunnels are in place, we might as well use them for subways. We’ll build them to be sea water proof by design, so that the time and cost of pumping them out and putting them back into service will be minimal.

That’s the key!!! Instead of trying to think of ways to protect the tunnels, we should be building tunnels just to take storm surge – and making use of them between storms.